Method of making polymer



3,047,559 METHUD F MAKENG POLYMER Rowland H. Mayor, Stow, and Richard Leshin, Akron,

Ohio, and Bernard Wargotz, Long Branch, N.J., as-

signors to The Goodyear Tire & Rubber Company,

Akron, Ohio, a corporation of Ohio No Drawing. Continuation of application Scr. No.

564,121, Feb. 3, 1956. This application Sept. 11, 1961, Ser. No. 137,019

9 Ciaims. (Cl. 26094.3)

This invention relates to polymers derived from isoprene. More particularly, this invention relates to polyisoprene in which a major proportion of the isoprene residues have a cis configuration and to a method for preparing such polymers from isoprene.

Rubber and gutta percha are naturally-occurring high molecular weight materials which can be broken down into isoprene structural units by pyroylsis or destructive distillation. Although they have identical empirical formulas, X-ray diffraction studies show that these materials differ in the geometrical configuration or spatial arrangement of the atoms comprising their molecules. Rubber has been shown to have the cis form, which may be represented as and gutta percha has been shown to have the trans form, which may be represented as I on, o

Of the two forms, the cis form is the more valuable, and its use commercially runs into millions of pounds per year. Large plantations are operated to produce this form from latex-bearing trees, in particular the Hevea brasiliensis, which produces about 95% of the worlds natural rubber supply. Because rubber-producing trees require certain climatic conditions for their growth, they can be grown only in limited localities. Rubber is highly important to the life of modern civilization and is considered to be one of the essential raw materials for the production of both military and civilian goods. Because of its great industrial importance, there have been many efforts to make a substitute for rubber obtained from the Hevea brasiliensis. The production of rubber from other rubber-bearing plants has not been practical so far. The most successful substitute to date has been the synthetic copolymer of butadiene and styrene known as GRS rubber. This material, of course, does not have the same structure and properties as natural rubber, but it is a serviceable substitute for many purposes. It has not been possible, however, to produce satisfactory large truck tires from GRS because the heat caused by flexing and friction of the tires in use cannot be dissipated rapidly enough to prevent degradation of the tire. Natural rubber must be used for the production of large tires. 7

Many efforts have been made to produce another substitute which more closely resembles natural rubber. Such approaches as the polymerization of isoprene to polyisoprene by the usual methods, such as emulsion 3,047,559 Patented July 31, 1962 polymerization, have not been successful. The polymerization of isoprene by the usual methods produces a polymer which generally contains about 50% or more of the double bonds arranged in the trans configuration. This material is not suitable for use as a substitute for natural rubber.

It is an object of this invention to produce a synthetic rubber suitable for use in heavy duty tire applications. It is another object to produce a synthetic substitute for natural rubber. Another object, of this invention is to provide a method for polymerizing isoprene to form a polymer having a major proportion of the isoprene residues arranged in the cis structural form. Still another object is to provide a method of producing a synthetic polymer which has the physical characteristics of natural rubber. Still another object is to provide new chemical compositions composed of isoprene molecules united substantially completely in the 1,4 positions and having a action product of titanium tetrachloride and an organometallic compoundof the general formula in which R, is selected from alkyl, aryl and aralkyl groups and R and R are selected from alkyl, aryl and aralkyl groups and hydrogen, or an ether ate of such an organometallic compound.

The practice of the invention is illustrated by the following examples. The polymerization reactions described below were conducted in 4-ounoe screw cap bottles. The bottles were charged under an inert atmosphere and, after charging, were sealed with metal caps containing neoprene gaskets and Teflon linings. After sealing, the bottles were kept at the temperature indicated.

Example 1 Under a nitrogen atmosphere, 350 grams of ethyl bromide were added slowly to 60 grams of a 69/31 (weight ratio) aluminum-magnesium alloy, a reflux temperature being maintained. The addition was completed in four hours, and the temperature was raised to C. to insure complete reaction. After standing overnight, the product, diethylaluminum bromide, was distilled at 100 C. to 0.4 millimeter of mercury pressure, 193 grams (76% yield) being obtained. The product was added cautiously to 27 grams of sodium with warming. After an initial vigorous reaction, the reaction proceeded smoothly, the diethylaluminum bromide being added over a period of 2 hours at a temperature of -120 C. The mixture was then warmed slowly to 200-210 C. and maintained at that temperature for 2 hours. Distillation of the product at 75 C. and 1.6 millimeters of mercury pressure gave 64 grams (72% yield) of triethylaluminum.

Example 2 A mixture of 107.5 grams of diethylaluminum bromide (prepared as in Example 1), 34.4 grams of sodium fluoride and milliliters of hexane was refluxed for one hour under a nitrogen atmosphere. The hexane was removed by distillation, and the product, diethylaluminurn fluoride, was distilled at 97.5-1000" C. at 1 millimeter of mercury pressure. The distillate, which weighed 22 grams (32% yield) was heated further with 8.9 grams of sodium fluoride for 4 hours at -190" C. under nitrogen. Distillation at 85 C. and l millimeter of mercury pressure was very slow, yielding about 6 grams (37% yield) of triethyl aluminum in 1 /2 hours.

Example 3 A solution of 1 ml. of triethylaluminum (prepared by the method of Example 1) in 50 milliliters of hexane, in a 4-ounce bottle, was treated with 10 drops (0.25 milliliter) of titanium tetrachloride, giving a black precipitate. Twenty-five milliliters of isoprene were added, and the bottle was sealed and rotated in a 50 C. water bath for 16 hours. Very little reaction occurred, and the mixture was treated with an additional 0.2 milliliter of titanium tetrachloride and agitated at 50 C. for an additional 24 hours. The product was precipitated in isopropyl alcohol, containing a rubber antioxidant, and was treated to remove gel by dissolving the product in benzene, filtering and precipitating by pouring the henzene solution into isopropyl alcohol containing additional antioxidant. An infra-red spectral analysis on the purified rubber showed 96% cis-1,4 structure, 4% 3,4

structure, and no 1,2 or trans 1,4 structure.

Example 4 been caused by traces of diethylaluminum fluoride in the catalyst. A sample of this rubber was cross-linked using 1.5% by weight of decamethylene-bis-methylazo-dicarboxylate. This cross-linked product, when stretched, gave an X-ray diffraction pattern identical with that of natural Hevea rubber.

Example 5 Triethylaluminum (0.25 milliliter) under a helium atmosphere, was treated with 0.1 milliliter of titanium tetrachloride, immediately giving a brownish-black precipitate. The precipitate was suspended in milliliters of pentane and 10 milliliters of isoprene were added. After 17 hours at room temperature, the product formed was purified by the method used in Example 3, yielding 2.6 grams (38%) of gel-free polymer having an inherent viscosity of 1.72. A second sample similarly prepared gave 3.9 grams (57% yield) of purified rubber having an inherent viscosity of 1.511.

Example 6 Isoprene was polymerized as in Example 5, except for the use of approximately 0.1 milliliter of triethylalumimum and 0.03 milliliter of titanium tetrachloride in the catalyst system. After 1 hour at room temperature, the polymerization mixture had solidified. After removal of benzene-insoluble products, as above, 2.9 grams (42.5% yield) of purified rubber with an inherent viscosity of 1.2 were obtained.

Example 7 To the dark brown precipitate, formed by adding 0.1 milliliter of titanium tetrachloride to 0.25 milliliter of triethylaluminum, milliliters of isoprene were added. After 17 hours at room temperature, the mixture had solidified, and 1.4 grams of polymer, purified as in Example 3 (gel-free), were isolated.

Example 8 The precipitate formed by treating 0.25 milliliter of triisobutylaluminum with 0.1 milliliter of titanium tetrachloride was suspended in 10 milliliters of benzene. Ten

a milliliters of isoprene were added. After 20 hours at room temperature, 2.0 grams (29% yield) of crude rubber were isolated.

Example 9 To the precipitate formed by mixing 0.1 milliliter of triisobutylaluminum and 0.03 milliliter of titanium tetrachloride were added 10 milliliters of pentane and 10 milliliters of isoprene. After 2 4 hours at room temperature, 6.1 grams yield) of crude rubber were obtained.

Example 10 A series of polymerizations were carried out as indicated in the following table. In these experiments, the triisobutylaluminum and the titanium tetrachloride were mixed, the complex formed was dispersed in 25 milliliters of pentane, and 25 milliliters of isoprene were added to this dispersion. The bottles were allowed to stand at room temperature.

Milliliters of Milliliters of Yield of Experiment No. Triisobutyl Titanium Rubber Aluminum Tetrachloride (Percent) The volumes of titanium tetrachloride were measured by drops, and are approximate. In terms of mols, 0.25 milliliter of triisobutylaluminum is equivalent to approximately 0.11 milliliter of titanium tetrachloride. The polymer prepared with more than the equivalent quantity of titanium tetrachloride tended to contain considerable amounts of gel, while those with equivalent amount, or less, of titanium tetrachloride were softer and showed relatively little gel.

Example 11 To a mixture of 1.0 milliliter of triethylaluminum ethyl etherate and 0.5 milliliter of titanium tetrachloride were added 15 milliliters of hexane and 25 milliliters of isoprene. After 17 hours at 50 C., the polymerization mixture solidified. A low molecular weight rubber was isolated which gave an infrared spectrum similar to that of natural rubber.

The examples illustrate the practice of the invention with particular respect to the use of the triethylaluminumtitanium tetrachloride, triisobutylaluminum-titanium tetrachloride and triethylaluminum-ethyl etherate-titanium tetrachloride complex catalysts. Other organo aluminumtitanium tetrachloride and organo aluminum etheratetitanium tetrachloride complex materials can also be used. Representative examples of such complexes are the complexes formed by the reaction of titanium tetrachloride with organo aluminum compounds of the general formula R3/ in which R is selected from alkyl, aryl and aralkyl groups and R and R are selected from alkyl, aryl and aralkyl groups and hydrogen and with the etherates of these compounds. Representative examples of such compounds are ethylaluminum dihydride, n-propylaluminum dihydride, n-butylaluminum dihydride, isobutylaluminum diydride, phenylaluminum dihydride, p-tolylaluminum dihydride, benzylaluminum dihydride, diethylaluminum hydride, di-n-propylaluminum hydride, di-n-butylaluminum hydride, diisobutylaluminum hydride, diphenylaluminum hydride, di-p-tolylaluminum hydride, dibenzylaluminum hydride, phenyl ethylaluminum hydride, phenyl npropylaluminum hydride, phenyl isopropylaluminum hydride, p-tolyl ethylaluminum hydride, p-tolyl n-propylaluminum hydride, p-tolyl isopropylaluminum hydride,

aluminum dihydride diethyl etherate, isopropylaluminum dihydride di-n-"Jropyl etherate, phenylaluminum dihydride dibutyl etherate, p-tolylaluminum dihydride diisopropyl etherate, benzylaluminum dihydride diisobutyl etherate, phenyl ethylaluminum hydride diethyl etherate, p-tolyl ethylalurninum hydride diethyl etherate, benzyl ethylaluminurn hydride diethyl etherate, triethylalurninum diethyl etherate, triisobutylaluminum diethyl etherate, triphenylaluminum di-n-propyl etherate, tri-p-tolylalurninum dibutyl etherate and tribenzylaluminum diisopropyl etherate.

The etherates such as diethyl etherate are generally formed by reacting an organo magnesium halide with an aluminum halide in ether. They can also be formed by adding the organo altuninum compound to an ether.

The polymerization reaction can be run in mass, in solution, or by contacting vapor of the monomer with the catalyst. It is preferred to run the reaction in the presence of an inert diluent such as cyclohexane, hexane, pentane or benzene. Any suitable hydrocarbon material that is inert to the polymerization reaction and which does not react With the catalyst can be used. It is preferred to use the saturated hydrocarbon solvents. Various ratios of solvent to monomer can be used.

The organo aluminum compound/ titanium tetrachloride ratio can be varied over a wide range. Obviously, a sufiicient amount of the catalyst complex must be formed to cause polymerization, but the catalyst concentration can be varied over wide limits.

As is usual with polymerization reactions, the temperature at which the polymerization is carried out may be varied over a wide range. It is desirable to use a temperature which will give a practical rate of reaction and which will give a good yield of polymer in a reasonable time.

This application is a continuation of application Serial No. 564,121, filed February 8, 1956, now abandoned.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein Without departing from the spirit or scope of the invention.

What is claimed is:

1. A method which comprises polymerizing isoprene in the presence of a catalytic amount of a complex of titanium tetrachloride with an etherate of a compound selected from the group consisting of organo metallic compounds of the general formula in which R is selected from alkyl, aryl and aralkyl groups and R and R are selected from alkyl, aryl and aralkyl groups and hydrogen 2. A method w ich comprises polymerizing isoprene in the presence of a catalytic amount of a complex of titanium tetrachloride with a dialkyl etherate of a compound selected from the group consisting of organo metallic compounds of the general formula in which R is selected from alkyl, aryl and aralkyl groups and R and R are selected from alkyl, aryl and aralkyl groups and hydrogen, the alkyl groups attached on the ether oxygen containing from 1 to 5 carbon atoms.

3. The method of claim 2 in which the catalyst is a triethylaluminum diethyl etherate-titanium tetrachloride complex.

4. The method of claim 2 is which the catalyst is a triisobutylaluminum diethyl etherate -titanium tetrachloride complex.

5. The method of claim 1 in which the polymerization reaction is carried out in an inert solvent.

6. The method of claim 2 in which the polymerization reaction is carried out in an inert solvent.

7. The method of claim 5 in which the inert solvent is a hydrocarbon.

8. The method of claim 6 in which the inert solvent is a hydrocarbon.

9. The process for polymerizing isoprene which comprises forming a mixture of triethyl aluminum-ethyl etherate and titanium tetrachloride in which 0.5 volume of titanium tetrachloride is used per volume of triethyl aluminum-ethyl etherate, adding a mixture of 25 volumes of isoprene and 15 volumes of hexane per volume of triethyl aluminum-ethyl etherate used and carrying out the polymerization reaction at 50 C.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3JVL$ July 13;,

Roux/3on H. f1; cr e Ci.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5. lines :25 to 29 the formulr. shoul-j c 5 tea. 1'

i V I i shown Iucrow .anslwm. or as 1n the patent:

C K /H CH C C (3H,,

cur (31K c:c\

same column, lines 32 to 1 1-, the formula shoulu appear as shown below instead 0; as in the patent:

3 5 CH2 C ('3 C 2 ('3 Ch H H column 2, line 50, for "to" read at same column, line 68, for "1000 C." read 1o? C.

Signed and sealed this 26th day 01' February 1963.

(SEAL) Attest: 

1. A METHOD WHICH COMPRISES POLYMERIZING ISOPRENE IN THE PRESENCE OF A CATALYST AMOUNT OF A COMPLEX OF TITANIUM TETRACHLORIDE WITH AN ETHERATE OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ORGANO METALLIC COMPOUNDA OF THE GENERAL FORMULA 